A tire with radial carcass reinforcement comprises a crown zone surmounted radially on the outside by a tread designed to come in contact with the ground during the rolling of the said tire, with two sidewalls which extend the crown axially and radially on either side and which end in zones forming tire beads. The tire is then fitted on a mounting rim comprising rim seats of frustoconical or cylindrical shape which may or may not be extended by flanges, depending on the type of tire, these seats or flanges when present being extended by rim hooks of substantially circular shape.
The beads of the said tire come in contact with the seats and hooks of this mounting rim. The carcass reinforcement of the tire consists of a plurality of reinforcing elements (of cable or filament type, generally metallic) embedded in at least one rubber mix, the said reinforcing elements being orientated substantially in the meridian direction (i.e. in a direction making an angle close to 90° with the circumferential direction of the tire). To anchor the reinforcing elements in the tire bead, at least one circumferential bead reinforcement is provided and the carcass reinforcements can be turned up around the said bead reinforcement to form an upturn, or overlaid axially against the said reinforcement.
Under the combined action of the load carried by the tire and the rolling, the parts of the tire sidewalls near the footprint of the tire on the ground undergo cyclic variations of curvature. In this area the sidewalls undergo bending around the rim hooks in a meridian plane (i.e. a plane containing the rotation axis of the tire). Moreover, the compression of the tire engenders alternating and cyclic movements of the reinforcing elements of the carcass reinforcement in the sidewalls in the circumferential direction, which give rise to more or less substantial movement of the beads relative to the rim hooks. These movements are the larger, the greater is the load supported. The same applies when the tire size increases and also when the form ratio of the tire is small (H/S<1, where H is the height of the tire's cross-section and S is the width of the said cross-section).
Under the effect of these alternating movements in the circumferential and meridian directions, the beads rub against the hooks of the mounting rim and undergo wear to a greater or lesser extent. To reduce this wear, it is known, besides using rubber mixes that are less sensitive to frictional wear, to arrange in each bead at a greater or smaller height (i.e. radially towards the outside) in the sidewalls at least one additional reinforcement consisting of a plurality of reinforcing elements (metallic cables or wires) positioned next to one another and orientated at small or zero angle relative to the circumferential direction (small or zero angle is understood to mean an angle between 0° and 15°).
These reinforcing elements may be continuous, i.e. making at least one complete turn, or discontinuous, i.e. extending over an angular fraction of one turn smaller than 360°. The said additional reinforcement may be located axially inside or outside the carcass reinforcement or axially against the upturn when the carcass reinforcement is anchored by turning up for example around a bead wire.
When reinforcements are used which extend over an angular fraction smaller than 360° (such reinforcements being referred to as “discontinuous” in the present document), endurance problems associated with certain distributions of the ends of the discontinuous reinforcements can arise, bearing in mind the cycles of repeated stresses during rolling, described earlier.